Method for producing compacted articles having large length to diameter ratios



P 5, 1967 T. s. CLORAN ETAL 3,340,055

METHOD FOR PRODUCING COMPACTED ARTICLES HAVING LARGE LENGTH TO DIAMETERRATIOS Filed Dec.

8 N ,M R 0 L W C S 8 A M w T III] N 0 8 w 0 m R N 0 m w Attorney UnitedStates Patent ()fifice 3,340,055 Patented Sept. 5, 1967 ABSTRACT OF THEDISCLOSURE This invention relates generally to the art of powdermetallurgy and, more particularly, to a method for producing articlesfrom powdered metal having large length to diameter ratios, whereby saidarticles may be further reduced to final thicknesses by the use ofconventional rolling facilities. The method of the invention consists inthe steps of placing a charge of powdered metal in an elongated tubularcontainer, first compacting said container and charge by applying forcein a direction normal to the axis of said container while preventinglongitudinal extension thereof, second further compacting said containerand charge by applying force in a direction normal to the plane of saidfirst compacting force and the axis of said tubular container whilelongitudinal extension of the same is prevented, and finally compactingsaid container and charge to a final density of about 100 percent bysimultaneously applying positive pressure at both ends of said containerwhile the lateral spread thereof is restrained by a die. With the methoddescribed above, it is possible to produce from powdered metal, compactssuitable for rolling.

It is well known that by the use of powder metallurgy techniques, it ispossible to produce metal articles, such as high-alloy steel articles,of fine grain size and homogeneous microstructure. The conventionalpractice for producing articles of this type is to place a charge ofpowdered metal of, for example, 100 mesh within a closed container thathas been evacuated to a relatively low pressure, heat the container andcharge of powdered metal to an elevated temperature of, for example, atleast about 2000 F., compact the charge within the container by theapplication of suitable force while the charge is at elevatedtemperature, and finally remove the container from the compacted chargeby machining, pickling or a combination of both. After removing thecontainer from the compact, the compact may be either machined or forgedto form the desired final product. Because of the extremely highpressures required to achieve compacting to a density of 100 percent,only relatively small compacts having low length to diameter ratios havebeen produced. Since, to permit rolling in conventional facilities, theworkpiece must have a substantial length, for example at least about 42inches, the working of compacts produced by powder metallurgy techniquesto final products has been limited to forging and machining operations.

It is accordingly the primary object of this invention toprovide amethod for producing from powdered metal compacted articles having largelength to diameter ratios, which enables them to be processed to finalproducts by the use of conventional rolling facilities.

It is a further object of the invention to provide a method forproducing from powdered metal compacted articles having large length todiameter ratios without requiring excessive total compacting pressures.

These and other objects of the invention, as well as a completeunderstanding thereof, may be obtained from .the following descriptionand drawings, in which:

FIGURE 1 is a perspective view of the elongated tubular container forthe powdered metal to be compacted by the method of the invention;

FIGURE 2 is a diagrammatic showing of the first compacting step of themethod;

FIGURE 3 is a transverse sectional view of the compact and containerafter the first compacting step of the method;

FIGURE 4 is a schematic view of the second compacting step of themethod;

FIGURE 5 is a transverse sectional view of the compact and containerafter the second compacting step;

FIGURE 6 is a schematic showing of the final compacting step of themethod;

FIGURE 7 is a perspective view of the final compact; and

FIGURE 8 is a schematic showing of final compact being subjected to aconventional rolling operation.

With reference to the drawings, in the practice of the method of theinvention a charge of powdered metal, which has been thoroughly cleanedto remove surface oxides, is placed in a closed-end tubular container10, as shown in FIGURE 1. The container is then connected by means notshown, to a vacuum pump, whereby the container interior is evacuated toa pressure of, for example, 50 microns or less. On evacuation, thecontainer is heated to a temperature of at least, for example, 2000 F.Thereafter, the container 10 is placed within a die 12, as shown inFIGURE 2, and forces applied, as indicated by the arrows in FIGURE 2, toproduce a compact having a cross section as shown in FIGURE 3. As may beseen in FIGURE 2, the container 10 is confined Within the die 12 toprevent substantial longitudinal extension thereof during compacting.The compact is then placed within a die 14, as shown in FIGURE 4, and isfurther compacted by the application of force as indicated by the arrowsin FIGURE 4 to produce a compact having a cross section as shown inFIGURE 5. During this compacting operation, the die prevents substantiallongitudinal extension of the container. Thereafter, the compact, havinga sub stantially square cross section as shown in FIGURE 5, is placedwithin a die 16, as shown in FIGURE 6, wherein the cross section of thedie conforms substantially to that of the compact 10. Force is appliedin the form of positive pressure simultaneously at both ends of thecompact as indicated by the arrows in FIGURE 6. The die confines thecompact during this operation and prevents the lateral spread thereof.By applying positive pressure simultaneously from both ends of thecompact, the lateral forces during compacting are evenly distributedalong the length of the compact. This results in a compact characterizedby extremely uniform density from end to end. The final compact, asshown in FIGURE 7, after final compacting, as described above, has adensity of about percent. As also described above, its length todiameter ratio permits it to be processed as a conventional billet bythe use of rolling facilities typically employed for billet rolling.Prior to this operation, the container 10 will be removed by acidpickling or machining. As shown in FIGURE 8, compact 10 is passed bymeans of convyeor rolls 17 longitudinally between a pair of horizontalwork rolls 18, which in a conventional manner serve to reduce thecompact to a desired final thickness. It is to be understood, of course,that during the above-described compacting operations, it is customarythat the container and powered metal charge therein are maintained atelevated temperature.

As a specific example, in the practice of the invention, a mild-steelpipe having a Ai-inch wall thickness, an inside diameter of 10 inches,and a length of about 50 inches was filled with a charge of 100 meshAISIMZS steel powder. The container and charge of powdered metal wereheated to a temperature of approximately 2200 F. while the container wasevacuated to a pressure of about 25 microns. Thereafter, the containerand charge were subjected to initial compacting as described above withreference to FIGURE 2, to produce an intermediate compact having a widthof approximately 12 inches and a thickness of about 6- inches. Asdescribed above, the longitudinal extension of the container wasprevented during this compacting operation. During this initialcompacting operation, the density of the charge was increased from aninitial density of about 65 percent to a density of about 80 percent.Because of the low compacting densities required by this operation,compacting pressures of only 4 tons per square inch were required. Thecompact was then subjected to the second operation as shown in FIGURE 4and described above, to achieve a compact of substantially square crosssection of about 7 /2 inches. During this compacting step, the densityof the compact was increased from the starting density of 80 percent toa density of about 95 percent. During this operation, pressures of about4 tons per square inch were required. The compact was then placed on endwithin a die conforming substantially to the cross section of thecompact along its entire length, and positive pressure, through the useof two rams, was simultaneously applied at both ends of the compact. Bythe application of pressure on the order of 20 tons per square inch, afinal compact having a density of substantially 100 percent wasachieved. The length of the final compact was about 47 /2 inches, whichwas suitable for subsequent reduction by the use of conventionalbillet-rolling facilities.

Examination of the compact after the final compacting step showed thesame to have a substantially uniform density from end to end. This iscaused by the extremely even distribution of lateral forces during thefinal compacting operation. Although, during the first two compactingoperations pressure must be applied over a large surface area, the lowpressures per unit area necessary to produce the relatively lowintermediate densities required avoid the necessity for extremely highcapacity presses. During the final compacting to the required final 100percent density, extremely high pressures on the order of 20 tons persquare inch are required; however, the surface area over which thesehigh pressures must be applied is extremely small. Consequently, therequirement for extremely high capacity presses is again avoided.

During the practice of the invention as described above and shown in thedrawings, during the first compacting operation, wherein compacting isachieved by applying force in a direction normal to the axis of thecontainer, a compact density of at least about 80 percent is produced.During the second compacting step, wherein compacting forces applied ina direction normal to the plane of said first compacting force and theaxis of said container, a density of at least about 95 percent isachieved. During final compacting, wherein compacting is achieved bysimultaneously applying positive pressure at both ends of the containerwhile the lateral spread thereof is restrained by a die, a density ofsubstantially 100 percent is achieved. It is possible to eliminate thefirst compacting step by charging a container having a cross section asshown in FIGURE 3 with powder of a density permitting compacting to thedesired final density by using only the second and final step as setforth above. During the entire compacting operation, the container andcharge are, of course, at elevated temperature and at a pressuresubstantially less than atmospheric, preferably less than 25 microns, asdescribed above. During the first two compacting steps, the longitudinalextension of the container and charge is, of course, prevented. For thispurpose, the container is confined within a die during compacting. Tofacilitate processing of the final compact by conventional billetrolling facilities, a final compact having a substantially square crosssection is preferred.

Although various embodiments of the invention have been shown anddescribed above, it is obvious that other modifications and adaptationsmay be made without departing from the scope and spirit of the appendedclaims.

What is claimed is: I

1. A method for compacting metal powders to produce a compacted articlehaving a length substantially greater than the cross sectional diameterthereof comprising placing a charge of powdered metal precompacted to adesired density and, to be further compacted into an elongated article,by placing said precompacted charge into a container, first compactingsaid charge by applying force in a direction normal to the axis of saidelongated container, further compacting said charge by applying forceaxially to said elongated container, and removing said article from saidcontainer, said container being confined in a die during each compactingoperation.

2. A method for compacting metal powders to produce a compacted articlehaving a length substantially greater than the cross sectional diameterthereof comprising placing an uncompacted charge of powdered metal to becompacted into an elongated container, first compacting said charge byapplying force in a direction normal to the axis of said elongatedcontainer, second further compacting said charge by applying force in adirection normal to the plane of said first compacting force and to theaxis of said tubular container, further compacting said charge byapplying force axially to said elongated container, and removing saidarticle from said container, said container being confined in a dieduring each compacting operation.

3. A method according to claim 2 wherein the longitudinal extension ofsaid charge and container is restrained by said die during compacting.

4. A method according to claim 2 wherein said charge during said secondfurther compacting is compacted to a substantially square cross section.

5. A method according to claim 2 wherein said charge is compacted to adensity of at least about percent by said first compacting, to a densityof at least about percent by said second further compacting, and adensity of substantially percent by said final compacting.

6. A method according to claim 2 wherein said final compacting iseffected by simultaneously applying positive pressure at both ends ofsaid container while the lateral spread thereof is restrained by a die,whereby the result ing lateral forces are distributed substantiallyevenly along the length of said container.

7. A method according to claim 2 wherein said container is at elevatedtemperature and at a pressure substantially less than atmospheric duringcompacting thereof.

8. A method according to claim 7 wherein said con tainer is at anelevated temperature of at least about 2,000 F.

9. A method according to claim 2 wherein the thickness of said articleis reduced after final compacting by a rolling operation.

10. A method for compacting metal powders to produce a composite articlehaving a length substantially greater than the cross sectional diameterthereof comprising placing a charge of powdered metal to be compactedinto an elongated tubular container, first compacting said charge byapplying force in a direction normal to the axis of said container,while the same is confined within a die, to a density of at least about80 percent, second further compacting said charge by applying force in adirection normal to the plane of said first compacting force and theaxis of said tubular container, while the same is confined within a die,to a density of at least about 95 percent, further compacting saidcharge to a density of about 100 percent by simultaneously applyingpositive pressure at both ends of said container while the lateralspread thereof is restrained by a die, whereby the resulting lateralforces are distributed substantially evenly along the length of saidcontainer, said container being at an elevated temperature of at leastabout 2,000 F. and at a pressure substantially less than atmosphericduring compacting, removing said article from said container, andreducing the thickness of said article by a rolling operation.

11. A method for compacting metal powders to produce a compacted articlehaving a length substantially greater than the cross sectional diameterthereof comprising placing a charge of powdered metal to be com pactedinto an elongated container, first compacting said charge by applyingforce in a direction normal to the axis of said elongated containerwhile substantially restricting the longitudinal extension thereof,further compacting said charge by simultaneously applying positivepressure at both ends of said container while the lateral spread thereofis restrained by a die, whereby the resulting lateral forces aredistributed substantially evenly along the length of said container,removing said article from said container, and reducing the thickness ofsaid article by a rolling operation.

References Cited UNITED STATES PATENTS 2,386,604 10/ 1945 Goetzel 75-214X 3,075,244 1/ 1963 Glenn 75-214 X

2. A METHOD FOR COMPACTING METAL POWDERS TO PRODUCE A COMPACTED ARTICLEHAVING A LENGTH SUBSTANTIALLY GREATER THAN THE CROSS SECTIONAL DIAMETERTHEREOF COMPRISING PLACING AN UNCOMPACTED CHARGE OF POWDERED METAL TO BECOMPACTED INTO AN ELONGATED CONTAINER, FIRST COMPACTING SAID CHARGE BYAPPLYING FORCE IN A DIRECTION NORMAL TO THE AXIS OF SAID ELONGATEDCONTAINER, SECOND FURTHER COMPACTING SAID CHARGE BY APPLYING FORCE IN ADIRECTION NORMAL TO THE PLANE OF SAID FIRST COMPACTING FORCE AND TO THEAXIS OF SAID TUBULAR CONTAINER, FURTHER COMPACTING SAID CHARGE BYAPPLYING FORCE AXIALLY TO SAID ELONGATED CONTAINER, AND REMOVING SAIDARTICLE FROM SAID CONTAINER, SAID CONTAINER BEING CONFINED IN A DIEDURING EACH COMPACTING OPERATION.